fix(edit-history): review round 2 — whole lines around skipped ones, full-budget reads, orphan sweep

- Forward: after a line longer than the budget, the next line is read from
  its start instead of being skipped with it when it crosses the chunk end.
- Backward: the line before a skipped long line is read whole; a floor that
  turned out to be a line start no longer stalls.
- A chunk the shared forward budget cut short is not applied (it read as one
  over-long line) but read in a later pass, so a first open of a long main
  transcript reaches the subagents in the same sync.
- Load older reads a full budget block of up to three transcripts per click,
  taking turns, instead of splitting one budget (a normal Write longer than
  the share was skipped for good).
- A subagent transcript that vanished loses its cursor, so Load older does not
  stay on forever.
- POST /api/cleanup-state forgets the history of every record it drops; a
  startup sweep deletes edit-history files no session or record owns and
  stale tmp files of other processes.
- load() rebuilds entries from known fields (string diff lines, per-edit cap
  re-applied, ids counted against the byte cap), bounds pending Bash fields
  and agent ids, and does not parse a file over 32 MiB.
- No re-read after Codeman's own keep-alive turn.
- Tests: regression tests for each of the above (they fail on the previous
  commit); the remove-during-write test now meets the write under way; the
  sync and route tests remove their stores before the temp dir, so no late
  save recreates it in /tmp.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/api-reference.md

@@ -1087,13 +1087,13 @@ Lists are capped (300 files and 50 commits per repository) while the counts stay
 
 What the Edit history panel reads (Settings → Header & Panels → Header, per-device, default off): the edits a **local claude session** made, main agent and subagents, read from its transcripts. Read-only. Every route resolves the session through `findSessionOrFail` (another user's session is `404`). Remote, Docker and non-claude sessions answer `state: 'unsupported'` and are never read.
 
-`GET /api/sessions/:id/edits[?sync=1]` lists the stored edits, newest first, without diffs: `{ state, reason?, backfillTruncated, agents, entries }`. With `sync=1` it first reads what the transcripts gained since the last read; without it the server reads nothing. `state` is `ok`, `unavailable` (stored entries only; `reason` is `no-transcript` before the session has a transcript Codeman can find, or the read error; the transcript is the one the session's hooks report, else the newest `<id>.jsonl` under the session's `CLAUDE_CONFIG_DIR` override or the server's config dir) or `unsupported` (`reason`: `remote`, `docker`, `mode`). Each entry is `{ id, ts, path, relPath, kind: 'code'|'image', tool, created, added, removed, truncated, agentId? }`, where `tool` is the edit tool, `bash` for an image a Bash call produced or `sent` for one the agent sent; `relPath` is relative to the workspace (a subagent's worktree for its edits). `agents` maps a subagent id to `{ description, agentType, worktreeBranch? }`. `backfillTruncated: true` means older edits can still be loaded.
+`GET /api/sessions/:id/edits[?sync=1]` lists the stored edits, newest first, without diffs: `{ state, reason?, backfillTruncated, agents, entries }`. With `sync=1` it first reads what the transcripts gained since the last read; without it the server reads nothing. `state` is `ok`, `unavailable` (stored entries only; `reason` is `no-transcript` before the session has a transcript Codeman can find, `removed` once the session's history was deleted, or the read error; the transcript is the one the session's hooks report, else the newest `<id>.jsonl` under the session's `CLAUDE_CONFIG_DIR` override or the server's config dir) or `unsupported` (`reason`: `remote`, `docker`, `mode`). Each entry is `{ id, ts, path, relPath, kind: 'code'|'image', tool, created, added, removed, truncated, agentId? }`, where `tool` is the edit tool, `bash` for an image a Bash call produced or `sent` for one the agent sent; `relPath` is relative to the workspace (a subagent's worktree for its edits). `agents` maps a subagent id to `{ description, agentType, worktreeBranch? }`. `backfillTruncated: true` means older edits can still be loaded.
 
 `GET /api/sessions/:id/edits/:entryId` returns one edit's diff as unified text: `{ diff, truncated }` (each edit's diff is capped at 64 KiB). `404` for an edit the session does not have.
 
-`POST /api/sessions/:id/edits/older` reads the next older block of every transcript (main and subagents share the read budget) and answers like the list.
+`POST /api/sessions/:id/edits/older` reads the next older block of up to three transcripts, a full read budget each (with more transcripts, main and subagents take turns), and answers like the list.
 
-The edits are stored per session in `~/.codeman/edit-history/<id>.json` (mode 0600, at most 500 edits and 4 MiB of diff text, the oldest dropped), deleted when the session's record is removed (a killed pinned session keeps it) and never fed into `/api/v1/search`. No route here serves a file: the panel shows thumbnails through `file-raw` inside the workspace only; an image outside it opens in the file preview, which registers it through the attachment route.
+The edits are stored per session in `~/.codeman/edit-history/<id>.json` (mode 0600, at most 500 edits and 4 MiB of diff text, the oldest dropped), deleted when the session's record is removed (a killed pinned session keeps it; at startup, a file whose session no longer exists is deleted too) and never fed into `/api/v1/search`. No route here serves a file: the panel shows thumbnails through `file-raw` inside the workspace only; an image outside it opens in the file preview, which registers it through the attachment route.
 
 ## Git worktrees of a case